Alicella gigantea feeding (Photo By Alan Jamieson – Sent by author, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=166054547)

Dear Readers, when I first saw photos of this enormous crustacean feeding at the bottom of a deep sea trench, I was very impressed. Alicella gigantea can grow up to 34 centimetres long, and is an example of what’s known as ‘abyssal gigantism’ – the tendency of some deep sea creatures to be much larger than their shallow water equivalent (you might remember my recent piece on the Giant Squid). Why this particular animal should be so much larger than the prawns which end up in an appetiser is a subject that is open for debate – it could be that the larger size is an adaptation to the cold temperatures in the deep sea, or to increased oxygen levels in cold water.

Another possible explanation is that larger animals are able to forage over larger distances when food is scarce – Alicella lives exclusively (as far as we can see) on carrion. When a sea creature dies, it sinks to the bottom of the ocean, where a whole host of decomposers and detritivores are waiting to feed on it. However, as the corpse travels down to the abyssal depths, lots of other creatures will be eager to make use of the food value that it contains. Something which actually makes it into the deep sea (and Alicella has only been found at depths between 13,000 and 29,000 feet) is going to be a very rare occurrence. It’s been found that this animal lives in the deep sea in both the Pacific and Atlantic oceans, and that all the individuals found so far are very closely related, so presumably much of Alicella’s life is spent searching for food over a large area. Interestingly, Alicella has a specialised gut microbiome, with a large proportion of probiotic bacteria – this may protect it against some of the bacteria found in carrion.

Alicella found at 7,000 metres in the Kermadec trench (Photo By Alan Jamieson – Sent by author, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=166054541)

Most amphipods are red or orange in colour, which is thought to help them to evade predators. Alicella, however, is white, an indication that the animal is too large to be tackled by most deep-sea predators. There is evidence that it grows very quickly, but also that it has a long lifespan (at least ten years, which is ancient for a shrimp). It seems to be a very successful animal, going about its business as it probably has for millenia. Who knows what else is living in these places that we are only just starting to explore?

You can read more about Alicella here. And for 45 seconds of giant amphipod action at the bottom of the Mariana Trench, you can click here.